In-flight icing is a major concern in aircraft safety and a non-negligible source of incidents and accidents, and is still a serious hazard today. It remains consequently a design and certification challenge for aircraft manufacturers. The aerodynamic performance of an aircraft can indeed degrade rapidly when flying in icing conditions, leading to incidents or accidents. In-flight icing occurs when an aircraft passes through clouds containing supercooled water droplets at or below freezing temperature. Droplets impinge on its exposed surfaces and freeze, causing roughness and shape changes that increase drag, decrease lift and reduce the stall angle of attack, eventually inducing flow separation and stall. This hazardous ice accretion is prevented by the use of dedicated anti-icing systems, among which hot-air-types are the most common for turbofan aircraft. This work presents a methodology for the optimization of such aircraft hot-air-type anti-icing systems, known as Piccolo tubes. Having identified through 3D Computational Fluid Dynamics (CFD) the most critical in-flight icing conditions, as well as determined thermal power constraints, the objective is to optimize the heat distribution in such a way to minimize power requirements, while meeting or exceeding all safety regulation requirements. To accomplish this, an optimization method combining 3D CFD, Reduced-Order Models (ROM) and Genetic Algorithms (GA) is constructed to determine the optimal configuration of the Piccolo tube (angles of jets, spacing between holes, and position from leading edge). The methodology successfully results in increasingly optimal configurations from three up to five design variables. / Le givrage en vol constitue encore et toujours un souci majeur de sûreté en aviation et demeure une source non négligeable d'incidents et d'accidents. Ainsi, le givrage en vol reste un défi de taille en termes de conception et de certification pour les constructeurs aéronautiques. Les performances aérodynamiques d'un avion peuvent en effet se dégrader rapidement quand il vole en conditions givrantes, et ainsi engendrer des incidents ou même des accidents. Le givrage en vol a lieu quand un avion traverse des nuages contenant des gouttelettes d'eau surfondues à des températures inférieures ou égales au point de congélation. Les gouttelettes impactent sur les zones exposées et gèlent, ce qui augmente la rugosité, provoquant une augmentation de la traînée, une diminution de la portance et de l'angle de décrochage, et induisant éventuellement la séparation de l'écoulement et le décrochage. L'accrétion de glace est empêchée par l'utilisation de systèmes dédiés d'antigivrage, parmi lesquels les systèmes à air chaud sont les plus utilisés par les avions de ligne. Cet ouvrage présente une méthodologie en vue de l'optimisation de tels systèmes d'antigivrage à air chaud appelés tubes Piccolo. Ayant identifié les conditions de givrage en vol les plus sévères à l'aide de la CFD (Computational Fluid Dynamics, ou simulation numérique en dynamique des fluides) tridimensionnelle ainsi que les contraintes de puissance thermique liées au système de dégivrage, l'objectif est d'optimiser la distribution de chaleur de façon à minimiser la puissance thermique requise, tout en satisfaisant aux réglementations de sûreté en vol. Dans ce but, une méthode d'optimisation combinant la CFD 3D, la Modélisation d'Ordre Réduit (MOR) et les Algorithmes Génétiques (AG), est développée afin de déterminer la configuration optimale du tube Piccolo (en termes d'angles de jets, de distance entre les jets et de distance au bord d'attaque). Cette m

The effectiveness of using a half delta wing tip strake for static wing tip vortex control and performance enhancement was investigated. The flowfield over the wingtip and in the near-field was studied over a low aspect ratio NACA 0012 wing fitted with a half delta wing with a leading-edge sweep of 64º at a chord Reynolds number of 3 x 10⁵. The incidence of the strake relative to the main wing was movable allowing for strake settings from δ = -10º to +10º. Force balance data supplemented with flowfield measurements were used to investigate the performance improvements with the addition of the strake and to understand the interaction between main wing and strake. Velocity and vorticity fields were compared to the clean rectangular planform wing (baseline wing), a sharp 64º sweep half delta wing and full delta wing for direct comparison and to better understand the flow physics involved. The effect of streamwise location, angle of attack and strake setting were examined. Particular attention was paid to the strength, size and development of the strake vortex and ensuing trailing vortex. It was found that the strake behaves much like a delta wing albeit with a strengthened LEV that prematurely breaks down. The broken down LEV then results in a tip vortex which is much more diffused than its baseline counterpart. In order to quantify this effect, the Maskell model was used to calculate the induced drag of both the baseline wing and the strake equipped wing at various angles of attack and strake settings. The results indicated that the addition of the strake reduces the induced drag particularly at high lift coefficient. / Une étude a été faite sur l'efficacité d'utiliser une aile demi-delta comme apex de bout pour le contrôle du tourbillon marginal d'une aile stationnaire ainsi que pour l'amélioration de la performance. Le champs d'écoulement dessus le bout de l'aile et dans le champs proche a été étudié utilisant une aile de profil NACA 0012 avec une petite allongement équippée d'une aile demi-delta d'angle 64º à un nombre de Reynolds de corde de 3 x 10⁵. L'incidence de l'apex en relation avec l'aile principale était amobile, permettant des positions d'incidence de l'apex de δ = -10º à +10º. Des données prises avec une balance supplémenté avec des mesures dans le champs d'écoulement ont été utilisées pour étudier les améliorations de performance avec l'addition de l'apex et pour comprendre l'intéraction entre l'aile principale et l'apex. Les champs de vitesse et de vorticité ont été comparés aux résultats avec une aile de voilure rectangulaire (aile de base), une aile demi-delta d'angle 64º et un bord d'attaque aiguë et une aile delta pour une comparaison directe et pour mieux comprendre les physiques des écoulements impliquées. L'effet de la position longitudinale, de l'incidence et de la position d'incidence de l'apex ont été examinés. On a particulièrement porté attention sur la puissance, la taille et le développement du tourbillon de l'apex et le tourbillon marginal résultant. On a trouvé que l'apex se comporte comme une aile delta, mais avec un tourbillon de bord d'attaque plus puissant qui cause l'éclatement tourbillonaire prémature. Conséquemment le tourbillon de bord d'attaque éclaté devient un tourbillon marginal qui est beaucoup plus diffusé que l'aile de base. Pour quantifier cet effet, le modèle de Maskell a été utilisé pour calculer la trainée-induite de l'aile de base et de l'aile equippée de l'apex à une variété d'incidences et de positions d'incidence de l'apex. Les résultats ont indiqué que l'addition de l'apex réduit la trainée-induite particulièrement quand les coefficients de portance sont élevés.

Satellite formation flying is a very promising field for future space missions as it holds many advantages over the common monolithic satellite. However, in order for the formations to be effective, a formation maintenance scheme is required to overcome perturbations arising from different sources. In this thesis the effect of atmospheric drag on a formation is examined. To do so the Schweighart and Sedwick equations, which describe the motion of a spacecraft, called deputy spacecraft, relative to another spacecraft, referred to as the chief spacecraft, placed in a circular orbit, are modified to account for atmospheric drag. The modified equations keep the effects arising from the oblateness of the Earth, known as the J2 effects, which were included in the model proposed by Schweighart and Sedwick. A similar set of equation is then developed for satellite formations placed in orbits of small eccentricity. A formation maintenance scheme which uses differential atmospheric as a means of control is then introduced. Numerical simulation results showing the evolution of formations through time with and without active control are also provided. / Le vol de satellite en formation est un domaine très prometteur pour de futures missions spatial étant donnés les nombreux avantages que cette technologie détient le satellite monolitique commun. Toutefois, pour que ces formations soient efficaces, un système de maintenance de formation est nécessaire pour surmonter les perturbations provenant de multiples sources. Dans cette these, l'effet du freinage atmosphérique sur une formation est examiné. Pour ce faire, les equations de Schweighart et Sedwick, qui décrivent le mouvement d'un engin spatial, appelé meneur, relative à un autre engine, nommé suiveur, place sur une orbite circulaire, sont modifiées pour tenir compte du freinage atmosphérique. Les equations modifiées conservent les effets découlant du fait que la Terre n'est pas parfaitement sphérique, connus comme les effets J2, qui sont inclus dans le modèle proposé par Schweighart et Sedwick. Un ensemble d'équations similaire est ensuite développé pour des formations de satellites placées sur des orbites de petites eccentricités. Un système de maintenance de formation qui utilise le freinage atmosphérique comme moyen de contrôle est introduit. Des resultats de simulations numériques montrant l'évolution dans le temps de formations avec et sans contrôle sont également fournis.

There is a resurgent interest in the use of airships for long-endurance and heavy-lift operations, as they provide an energy-efficient means of transportation for missions in which speed is not critical. Autonomous unmanned airships that are capable of flying a predefined path without human interaction can be used for a variety of missions, from wildlife monitoring to civil security tasks. This work investigates the control aspects of a novel, finless airship design with the goal of autonomous operation.In a first step, the dynamics of a finless airship are analysed. The conservative forces acting on the airship hull are derived via a Newton-Euler approach and compared with the literature. The non-conservative forces applicable to the vehicle studied here are taken from the literature to complete the equations of motion. A simulation of the airship dynamics including a detailed sensor noise and actuation model is built as a basis for the controller design.Two different control strategies, linear $H_\infty$ control and non-linear Backstepping control, are investigated for the stabilization of the attitude and velocity of a finless airship. After achieving satisfactory results in the simulation, the controller based on the nonlinear Backstepping technique is also used in flight tests, exhibiting good control performance.To enable trajectory tracking, a separate high-level controller is developed that allows trajectory tracking and hover with a single control law. The high-level controller uses the nonlinear low-level controller for airship stabilization. The performance of this controller is first verified in simulation. Subsequent flight testing produced similar results as the simulation showing that the controller suite is robust to effects not modelled in the simulation.The last aspect of this work is the development of a wind estimation algorithm. This algorithm uses the observed airship motion to calculate an estimate of the wind speed without the need for additional sensors, such as airspeed sensors. Having wind information available allows improvement of controller performance, as the airship dynamical response to control inputs can be predicted more precisely. / Depuis quelques années, il y a un renouvellement de l'intérêt pour l'utilisation des dirigeables pour des missions de longue durée ou pour les opérations avec des poids lourds. Les dirigeables offrent un moyen de transport efficace pour des missions pour lesquelles la vitesse n'est pas essentielle. Des dirigeables non pilotés et autonomes qui sont capables de suivre un trajet prédéfini sans aucune intéraction humaine peuvent être utilisés pour des missions diverses, comme par exemple l'observation des animaux sauvages ou des tâches concernant la sécurité civile. Cette thèse recherche les aspects de contrôle pour un nouveaux concept de dirigeable sans stabilisateurs avec le but d'une opération autonome.Comme première étape, les dynamiques d'un dirigeable sans stabilisateurs sont analysées. Les forces conservatrices qui agissent sur l'enveloppe du dirigeable sont dérivées en utilisant la méthode de Newton-Euler et elles sont comparées avec la littérature. Les forces non-conservatrices applicables au véhicule utilisé dans cette thèse sont pris de la littérature pour compléter les équations dynamiques. Une simulation de la dynamique du dirigeable est développée comme base pour le développement des contrôleurs. Cette simulation inclut des modèles detaillés pour le bruit des capteurs et les dynamiques des actuateurs. Deux stratégies de contrôle différentes sont investigées pour la stabilisation de l'assiette et la vitesse du dirigeable: la technique de contrôle linéaire $H_\infty$ et la technique de contrôle non-linéaire backstepping. Après avoir obtenu des résultats satisfaisants dans les simulations, le contrôleur utilisant la technique backstepping est aussi vérifié en essais en vol, démontrant une bonne performance. Pour être capable de suivre un trajectoire, un contrôleur supérieur qui est capable de suivre un trajectoire et de maintenir une position fixe avec une seule loi de contrôle est développé. Le contrôleur supérieur se sert du contrôleur backstepping pour la stabilisation du dirigeable. D'abord, la performance de ce contrôleur est vérifiée en simulation. Ensuite, les essais en vol donnent des résultats similaires à la simulation, démontrant que les contrôleurs sont robustes pour les effets non-simulés.Le dernier aspect de cette thèse est le développement d'un algorithme pour l'estimation du vent. Cet algorithme utilise le mouvement observé du dirigeable pour déterminer un estimé du vent sans avoir besoin de capteurs additionnels. Connaître le vent permettra d'améliorer la performance du contrôleur parce que la réponse dynamique du dirigeable aux changements de l'assiette peut être mieux prévue.

This thesis presents the quasi-rigid body formulation, a framework for viewing a satellite formation as a single entity. The formulation attaches a coordinate frame to the formation, which is incorporated into the system dynamics using Newtonian and Lagrangian mechanics. Solutions to the dynamic model in terms of quasi-rigid body states show that natural and forced relative orbits are compactly described using the formulation. Control of a formation can effectively be separated into a torque to control the orientation, and forces to maintain formation rigidity. Two closed-loop controllers are designed. One uses Lyapunov stability theory. The other prescribes a schedule of linear feedback matrices. Both act upon a formation as a whole. Simulations show that the controllers can be used to maintain formations and perform constrained reorientations while in Earth orbit. For formations in deep space, the formulation defines a more fuel-efficient reorientation trajectory than a rotation about the Euler axis. / Ce mémoire présente une approche de modélisation d'une formation de satellites en une masse quasi-rigide. Dans cette formulation, un système de coordonnées est défini sur la formation, et inclus dans les équations du mouvement selon les méthodes de la mécanique newtonienne et lagrangienne. Cette approche permet de résoudre les équations du mouvement et d'exprimer les orbites relatives naturelles et forcées de manière concise. On peut ainsi contrôler la formation avec des moments de force pour régler l'attitude et avec des forces pour maintenir la rigidité de la formation. Deux systèmes de contrôle ont été conçus. Le premier est basé sur la théorie de stabilité de Lyapunov. L'autre emploie une série de matrices en rétroaction négative. Ces deux approches permettent de contrôler la trajectoire des satellites en groupe. Les résultats démontrent que les systèmes de contrôle sont capables de maintenir les formations en orbite autour de la Terre et de changer leur orientation collective. Pour les formations de satellites dans l'espace lointain, la formulation définit des trajectoires de ré-orientation permettant une meilleure économie de carburant qu'une rotation autour de l'axe Euler.

Two explicit time-integration schemes based on a finite-volume approach for the solution of the Euler equations are developed and used in the study of compressible flows. The starting point is a comparison of the performance of three widely used methods (i.e., Jameson's, MacCormack's and Godunov's) in several rather difficult test problems, characterized by the existence of flow discontinuities or strong nonlinearities. This indicates that the best solutions for such flows are obtained when the numerical method is closely related to the physical behaviour of the fluid, as is the case with Godunov's method, in contrast with the other two methods, which need a special treatment of the discontinuities, and are very prone to numerically induced oscillations. Therefore, a first scheme, which improves the way Jameson's method computes the flux-node variables in that it treats in a more realistic manner the physics of signal propagation in both subsonic and supersonic flow, is developed. The numerical experiments with this scheme suggest that it converges more rapidly and does not need the dissipation terms, thus leading to computer efficiency and a gain in accuracy. The second method is a linear hybrid, in conservative form, between MacCormack's and Godunov's methods, which is shown to keep the best features of both the methods: second order accuracy in smooth regions of the flow and lack of oscillations near discontinuities, where it behaves locally like a first-order monotone scheme.

Airfoils with structural nonlinearities subject to two-dimensional subsonic flow may undergo aeroelastic instabilities even below the linear flutter boundary. This thesis studies the aeroelastic behaviour of airfoils accounting for structural nonlinearities. The feasibility and potential of a modern nonlinear dynamics approach to the understanding of the underlying dynamics is investigated. / Extensive numerical simulations were performed for a two-degree-of-freedom air-foil with a freeplay nonlinearity in the structural pitch moment and subject to two-dimensional incompressible inviscid flow. Different types of attractors were identified well below the linear flutter speed via numerical simulations of the system, and the existence of chaotic attractors was verified. Basins of attraction and bifurcation diagrams were constructed showing rather complex dynamics of the system below the divergent flutter boundary. In some cases physical explanations are given for the air-foil's behaviour. Effects of the airfoil and nonlinearity parameters, airfoil camber and angle of attack and the compressibility of the fluid on the results are also presented, and it is shown that the system response is very sensitive to many parameters. / Similar investigations are presented for an airfoil with either cubic, bilinear or hysteretic nonlinearities. In many cases, most notably where the airfoil is subject to small preload, small central stiffness and small hysteresis, chaotic motions are detected for a considerable range of speed. A period doubling route to chaos is obtained for the particular case of cubic nonlinearity. / Numerical simulations were also performed for an airfoil-aileron combination and an airfoil with active flutter control accounting for freeplay structural nonlinearities in the pitch or flap hinge moment. More complex dynamics and chaotic oscillations were obtained for these three-degree-of-freedom systems. For the case of a freeplay in the aileron hinge moment a quasi-periodic route to chaos was identified. / Various numerical methods were employed to solve the equations of motion. Similar results were obtained in terms of the bifurcations and the amplitude of oscillations for all the numerical methods, so verifying to some extent the different numerical methods employed. / The systematic investigation of the aeroelastic response of airfoils with structural nonlinearities showed the existence of complex dynamics, and for velocities well below the linear flutter boundary it was demonstrated that the motion can be stable or that the airfoil can oscillate in a periodic or chaotic manner. The aeroelastic response was shown to be highly dependent on the initial conditions and numerous airfoil, nonlinearity and flow parameters. The results suggest that for aeroelastic analyses of aerosurfaces a nonlinear investigation of precise models is necessary.

The thesis presents the analysis, based on velocity singularities, of the upswept finite span wings of various planforms and distributions of incidence. / The method of velocity singularities has been first introduced by Mateescu for the analysis of the flow past airfoils, based on the singular behaviour of the fluid velocity near the leading edge and ridges. / In this work, the method of velocity singularities is extended to determine the solution of the flow in the Trefftz plane normal to the uniform stream. / Velocity singularities are used to obtain directly the complex expression of the perturbation velocity in the cross-flow coordinates. The spanwise variation of the circulation is obtained by integrating the real part of the complex conjugate velocity in the Trefftz plane, and then is related to the local intensity of the circulation on the wing. / Two methods of solutions were developed, one applicable only for wings with symmetrical distribution of incidence, and a more general one applicable for both symmetrical and non-symmetrical distribution of incidence. / Both methods have been validated by comparison with Carafoli's solutions for symmetrical wings. Then the more general method has been used to obtain solutions for various wings with non-symmetrical distribution of incidence, such as the case of wings with anti-symmetrically deflected ailerons. / The method was proven to be more efficient and accurate than the comparable methods that are currently employed.

An experimental investigation is presented for the aeroelastic response of a two-degree-of-freedom airfoil positioned in an incompressible flow. In particular, the effects of cubic structural nonlinearities in the pitch degree-of-freedom are considered. These nonlinearities are introduced via a specially designed pitch cam, which permits different degrees of nonlinearity, as well as a linear system, to be obtained. / Several linear and nonlinear system tests are presented, and the results compared and analyzed. The effects of linear plunge stiffness on the stability of the aeroelastic system are discussed, and the nonlinear system response is studied for different degrees of cubic nonlinearity in pitch. / In several nonlinear system tests, limit cycle oscillations (LCO) are observed when the air speed is above the linear flutter speed. The effects of airfoil initial conditions and air speeds on the LCO amplitude, frequency, and convergence rate are studied. / The effective linear flutter speed is predicted using the so-called "flutter-margin" method for both the linear and nonlinear cases. The prediction results for the nonlinear cases are compared with those for the linear cases and with the actual flutter speed.

Tethered satellites systems have been studied for several decades from which the concept of tether-connected space manipulators developed. The advantages of such robots derive from the extensive reach that can be provided by the tether. This would benefit applications such as satellite repair and space debris removal. / This thesis first examines the dynamics of a tethered space manipulator as its end-effector traces a prescribed trajectory. The platform, to which the robot arm is attached, is postulated to be much larger than the other components of the system and is specified to follow a circular orbit around Earth. The tether is modelled as a straight rigid rod and the motion of the system is assumed to be restricted to the orbital plane. The tether tension is monitored to ensure that the tether is not subjected to compressive forces. / The system is also studied under torque restrictions; namely, the torques acting on the tether attachment points are set to zero. The possible trajectories traced by the end-effector of this constrained system are investigated. In addition, a method is outlined to determine a feasible end-effector path between two given points while satisfying the zero-torque constraint on the tether.